Nitro Gears 29 Spline Pinion Seal and Nut
 

So everytime I towed my popup I would get a small leak from the pinion seal in the rear 3rd member. Since I put Nitro 4.88 gears in my 97 4runner, the pinion is upgraded from the stock 27 spline to a 29 spline pinion. You also need to purchase a new flange kit to accept this 29 spline which also comes with a new seal and nut for the pinion. When it came to replace the rear pinion seal I forgot about the change and purchased the seal, part number 90311-38047, which is for the 27 spline pinion and will not fit the 29 spline. I had a tough time figuring out what I needed and I really wanted OEM parts. Ended up finding part number 90311-41009 which is the rear pinion seal for a 29 spline pinion, and the nut was part number 90177-22003. I believe I looked up a 2004 Tacoma to get these part numbers.

I think it was in 2003 that toyota changed the 27 spline pinion to a 29 spline in some of the rear 8" axles. So far I've driven about 1200 miles with about 250 miles of towing and not a drop of oil leaking. I'm making this post so that if in the future if I need to do this again I'll have the part numbers, and perhaps someone else with the same setup might find this info helpful. The kit that Nitro sells for the flange kit that includes the seal and nut, I cant say for sure that they use OEM seals. They looked very similar, but Nitro's seal didnt have the part number that the OEM has on it. About the only difference I could tell from the two.

I'll update this post later down the road when I've put more milage on it.

I am trying to upgrade to a Yukon 29 spline pinion now. I am running into some issues with the bearing being very tight. Did you have to change to different bearings with the change to the bigger 29 spline pinion?

I know this is a bit of a late response, but since I wasn't mentioned or quoted, I couldn't see it unless I looked at this thread. When I changed my gears, i also bought a master install kit which replaced all the bearings. I didnt do the install myself so I cant say for sure what the differences were.

I do want to update this on my pinion seal. No leaks at all with few more thousand miles on her.

Dude!! Thank you so much for this thread. I had been looking all over the internet to figure out what my problem was. I'd just figured out that the 29 spline conversion is what my problem was; however, I wanted to do more research before I banked on that conclusion. As far as I can tell, you're the only person who has figured it out and posted about it.

What is really confusing is that most other places say that the pinion seal on the 27 and 29 spline master install kits are the same for the Toyota 8", which gets really confusing. I am going to call Yukon tomorrow to figure out what is going on.

Here's the difference in specs I found when looking at pinion seals via O'reilley's:
Specs are almost the exact same but the 29 spline seal has a 0.2mm wider outside diameter, a 3mm wider inside diameter, and a 3mm wider shaft size.

To preface this: I run the 29 spline Yukon conversion kit paired with Yukon 4.56s and G2 master install kit. I had some play in my diff, so we swapped all the bearings with new a new G2 master kit. My guess is, the G2 kit is made for a 27 spline, which didn't agree with my 29 spline pinion; therefore, I had a leaky pinion seal. Because I had that leak, I swapped in a new 3rd gen seal from O'reilley's, which is profusely leaking now.

After hours of attempted research, I am now at your post... Keep in mind, East coast gear supply says their master kit is compatable with either. Yukon has one section that has a master install kit for -02' and down Toyota 8", which would be 27 spline; however, it also says it's compatible with 4th gens, FJs, and Gxs.... I'm not sure if that's a copy & paste thing or what, but it's confusing.

Long story short, thanks for this post!